On the Possibility of Using the Jellium Model as a Guide To Design Bimetallic Superalkali Cations

Abstract

The potential application of the jellium model as guidance in the rational design of bimetallic superalkali cations is examined under gradient‐corrected density functional theory for the first time. By using Li, Mg, and Al as atomic building blocks, a series of bimetallic cationic clusters with 2, 8, 20, and 40 valence electrons are obtained and investigated. As the corresponding neutral clusters tend to lose one valence electron to achieve closed‐shell states in the jellium model, these studied cations exhibit much lower vertical electron affinities (EAvert, 3.42–4.95 eV) than the ionization energies (IEs) of alkali metal atoms, indicating their superalkali identities. The high stability of these cationic clusters is guaranteed by their considerable HOMO–LUMO gaps and binding energies per atom. Moreover, the feasibility of using the designed superalkalis as efficient reductants to activate CO2 and N2 molecules and as stable building blocks to assemble ionic superatom compounds is explored. Therefore, this study may provide an effective method for obtaining various metallic superatoms with extensive applications on the basis of the simple jellium rule.

Recent Progress on the Design, Characterization, and Application of Superalkalis

“…With the deepening of superalkali study, some special approaches beyond the above strategies have been also proposed to design superalkalis in recent years . For example, the fluorination of superalkaline earth metal cations was used to design a new kind of cationic (M‐F) + (M=OLi 4 , NLi 5 , CLi 6 , BLi 7 , and Al 14 , see Figure ) fluorides with superalkali character in 2014 .…”

“…Previously reported Li 3 (IE=4.08±0.05 eV) also belong to this category. In addition, the jellium model can also be used as a guide to rationally design bimetallic superalkali cations . Sun et al.…”

“…Two different approaches are most commonly used. For the first one, the VEAs are computed by taking the energy difference between the cation and neutral cluster at the cation's geometry . For the other, the VEAs are obtained by the restricted outer valence Green function (OVGF) method .…”

“…First of all, the designed superalkali species need to be the global minima in the potential energy surface to serve as the promising targets for experimental synthesis. To realize this, the potential energy surfaces of complicated superalkalis can be explored by using several stochastic search procedures, including the Saunders “kick” method, coalescence kick (CK) approach,– gradient embedded genetic algorithm (GEGA) procedure, Molclus program, and so forth. Such methods generate structures randomly and facilitate the thorough exploration of unknown isomers much more easily than manual methods.…”

“…[37] Previously reported Li 3 (IE = 4.08 AE 0.05 eV) [40] also belong to this category.I na ddition, the jellium model can also be used as ag uide to rationally design bimetallic superalkali cations. [41] Sun et al proposed as eries of bimetallic cationic clusters with 2, 8, 20, and 40 valence electrons by using Li, Mg, and Al as atomic building blocks (see Figure 8). As the corresponding neutralc lusters tend to lose one valence electron to achieve closed shell states, all the studied cations exhibit low VEAs (3.42-4.95 eV).…”